➤Electrolyte Balance
Changes in the concentration of electrolytes in the body may be due to changes in the amount of water or the amount of electrolytes. Sodium is the most common of the cations that exists in the extracellular fluid. As it is excreted through urine, it's balance in body is maintained by kidney. When the amount of sodium is decreased, aldosterone production is increased and an increased amount of sodium is re-absorbed by kidney.
Changes in the concentration of electrolytes in the body may be due to changes in the amount of water or the amount of electrolytes. Sodium is the most common of the cations that exists in the extracellular fluid. As it is excreted through urine, it's balance in body is maintained by kidney. When the amount of sodium is decreased, aldosterone production is increased and an increased amount of sodium is re-absorbed by kidney.
➤Water Balance
Water constituents about 60 percent of adult human body weight. It is distributed in the body in 3 main compartments,
Blood Plasma-
5% of body weight.
Interstitial Fluid-
11% of body weight.
Intracellular Fluid-
44% of body weight.
Water is taken into the body through the alimentary canal and small quantity is also produced by the metabolic process in the body. Water is excreted from the body in the expired air, as a constituent of faeces, as sweat, through the skin and through urine.
The amount of water excreted in expired air and in faeces is fairly constant. Water excreted in the sweat in associated with the maintenance of body temperature. The balance between intake and output is maintained by the kidney.
Normally, fluid output is directly related to fluid intake.Water loss through kidney is rigorously controlled and varies from1000 to 1500 ml in 24 hours.This output is mainly controlled the antidiuretic hormone(ADH).This hormone is produced and released into the blood by the posterior labe of pituitary gland.
Although the antidiuretic hormone is an important mean by which the water balance of the body is maintained, it is not the only one. If there is an excess amount of any dissolved substance in the blood. It is excreted through the kidney and excess of water is excreted with it e.g. in case of untreated diabetes mellitus. Also if excess amount of electrolytes have to be excreted from the body.
The amount of water required for this purpose is increased.This may lead to dehydration but it is usually accompanied by acute thirst and increased water intake.
➤Maintenance of Blood pressure
The juxtaglomerular cells in the kidney are responsible for this this function. When the blood pressure decreases, It causes release of hormone renin by the kidney. Renin react with globulin in the blood and form angiotensin which in turn forms angiotensin-1
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